2007 Fiscal Year Final Research Report Summary
Molecular mechanism of promotive regulation of vitellogenin synthesis and spermatogenesis by GnRH neuron in scallop
| Project/Area Number |
17580153
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
General fisheries
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| Research Institution | Tohoku University |
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Principal Investigator |
OSADA Makoto Tohoku University, Tohoku University, Graduate School of Agricultural Science, Associate Professor (30177208)
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| Co-Investigator(Kenkyū-buntansha) |
PARHAR Ishiwar S. Nippon Medical School, Graduate School of Medicine, Lecturer (10271339)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Bivalve / Germ cell / Spermatogonium / Vitellogenin / GnRH / Estrogen / Estrogen receptor |
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| Research Abstract |
1. Mitotic activity of gonial cell of scallop was quantitatively detected using BrdU incorporation through sexual maturation. It was suggested that the pattern of proliferation of gonial cells can be divided into two phases: phase I; oogonia and spermatogonia slowly proliferate through the growing stage: phase II; oogonia develop into oocytes and spermatogonia begin to proliferate rapidly through the mature and spawning stages. The proliferation of gonial cells is likely under the different endocine controls in phase I and II. The spermatogonial proliferation at phase II was promoted by a mGnRH-like peptide, one of two types of GnRH, which were identified in the neuron of CNS of scallop and transported to the gonad via hemocytes. The GnRH-induced proliferation was mediated through GnRH receptor and subsequently through estrogen synthesis in the estrogenic cell in the gonad. Therefore, it seems that GnRH stimulates estrogen synthesis and release in the gonad, resulting in activation of mitosis of spermatogonia.
2. Oocyte growth based on vitellogenin (Vtg) synthesis and accumulation at phase II was progressively controlled by GnRH neuron in CNS. The same type of GnRH as in male stimulated estrogenic cell in the ovary and the synthesized estrogen promoted Vtg gene transcription in the auxiliary cell which is similar to a follicle cell. On the other hand, another type of GnRH-like neuro peptide, whish has been newly identified as VPF (vitellogenesis promoting factor), promoted Vtg protein translation from Vtg mRNA. Vtg gene expression mediated through an estrogen receptor (ER). ER cDNAs were identified in three kinds of bivalves including scallop and the genes were induced by their own ligand, estrogen, suggesting that estrogen signaling is likely amplified by auto-regulation mechanism and effectively transduced into the auxiliary cell to achieve a high vitellogenin gene expression, resulting in vitellogenin protein synthesis and oocyte growth.
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